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Full text of "The Cambridge Natural History"

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LUNGS AND DIAPHRAGM                             CHAP-
then a larger fourth, after which comes the dilated commence-
ment of the small intestine. The latter might be regarded as
a chamber of the stomach were it not for the fact that the ducts
of the liver and the pancreas open into it. This represents one
type of the Cetacean stomach, which seems to be found in all "Whales
except the Ziphioids. In the latter, the oesophagus opens into
the first compartment as usual; but the second division of the
stomach arises not close to the entrance of the oesophagus, but
at the opposite end. It would seem, therefore, as if the first
division of the stomach, found in most Whales, were missing in
Zipliioids. This way of looking at the matter is confirmed by
the fact that in Jfyperoodon a remnant of the missing first
stomach is found in the shape of a small diverticulum of the
oesophagus just before it enters the stomach.
The essential difference between the "Whale's and the Rumin-
ant's stomach is this: in the latter the stomach is primarily
divided into two portions, of which the first is non-digestive
and is clothed with oesophageal epithelium. The second, the
abomasum, is the digestive region. The first part is again
divided into three compartments. In the Whales, on the other hand,
it is the digestive part which is again subdivided, while if the
first part is divided it is not markedly so as in the Huminants.
The lungs are remarkable for their unlobulated character; in
this they agree with the lungs of the Sirenia. The thoracic
cavity in which they lie is barrel-shaped, and not, as is usual in
terrestrial mammals, boat-shaped, i.e. narrower sternally than
above. The alteration of the shape of the thoracic cavity is
associated with the aquatic life; so at any rate the fact that it is
also marked in Seals and even in the Otter seems to show. The
Whales are also characterised by the great obliquity of the
diaphragm, which is extremely muscular. In this character
again we find an agreement with the Sirenia, and also with
other aquatic mammals; it is not therefore a character of
Whales so much as evidence of an adaptation to the aquatic life.
The advantage is, it appears, in the increased capacity of the
thoracic cavity, and the consequent greater possibilities of expan-
sion of the lungs, which it must be remembered serve as
hydrostatic as well as breathing organs.
Borne of the internal arteries of Whales break up into
Their kidneys are tabulated; whether this has